The Group B cams can be installed without changing the valve spring heights. Install an SC or 964 cam and the spring heights have to move up 1 mm.The increased duration of the Group B cam will flow more mass over time since the valves are open longer. Same goes for the SC and 964 cams except that because of the greater lift, the cams are open longer yet.

Are you sure about that?. Many out there have installed SC and 964 cams with stock springs.

__________________Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.